Using isolated ischemic and anoxic heart preparations, studies are directed at elucidating the effect of adenosine, a naturally occurring myocardial nucleoside, on the well known catecholamine induced increase in cyclic AMP formation, glycogen phosphorylase activation and iontropic state. The mechanism(s) by which adenosine attenuates the catecholamine elicited metabolic and mechanical responses is being investigated. In addition, the effect of adenosine on other factors which influence cardiac mechanical and metabolic function is being studied.